Fallout 4 concept art
Of all the Melee weapons in the Fallout universe, the Shishkabab is perhaps by far the coolest. It's basically a refurbished katana outfitted with a small canister containing potent fuel, and multiple jets used to emit the blade with flames from the canister, adding fiery energy damage in addition to the blade's physical ballistic damage. It can be modded to have a few more flame jets to deal more energy damage. There is no need to search for fuel for this weapon, as has infinite supply.